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Hydrogen containers type IV should stand for severe operational conditions, such as temperature variations from −40 °C to 85 °C, and depressurisation from high-pressure above 95 MPa to near atmospheric pressure. There are experimental studies showing that container's liner, usually a thermoplastic material, can suffer blistering and buckling during depressurisation process. It has also been proved that elastomers under high-pressure conditions, which are submitted to a rapid depressurisation, can suffer the formation of cavities because of the dissolved gas. The formation of microscopic defects in thermoplastic materials because of rapid depressurisation is less common in scientific literature. In this paper, we evaluate by numerical means the maximum depressurisation rate a polymer sample can stand before cavitation occurs. By studying the influence of geometrical and pressure conditions, so as material's properties, we obtain algebraic equations that define maximal depressurisation rate. Results of present work serve to estimate performance of liner materials, with the scope of safe and fast container discharge.

Polymer materials subjected to gases at high-pressure can have issues during decompression. For instance, a sudden decompression can promote the formation of cavities inside the material. This phenomenon is known as cavitation or eXposive Decompression Failure (XDF). There is a body of scientific articles discussing different aspects of cavitation phenomenon, which indicate that the degree of damage is proportional to saturation pressure, depressurisation rate, and material thickness, among other parameters. In this article we propose a general approach by non-dimensional parameters to estimate the risk of cavitation. Numerical results were validated with bibliographic evidence of cavitation in polymers, for both thermoplastics and elastomers. Present results can be used as guidelines for design of systems involving polymers under high pressure, such as o-rings or liners in type IV hydrogen containers.

International audience; Energy harvesting is one of the most promising research areas to produce sustainable power sources from the ambient environment. Which found applications to attain the extensive lifetime self-powered operations of various devices such as MEMS wireless sensors, medical implants and wearable electronic devices. Piezoelectric nanogenerators can efficiently convert the vastly available mechanical energy into electrical energy to meet the requirements of low-powered electronic devices. Among the piezoelectric materials, poly (vinylidene fluoride) (PVDF) and its copolymers are extensively studied for the development of energy harvesting devices. Due to the outstanding properties such as high flexibility, ease of processing, long-term stability, biocompatibility makes them a promising candidate for piezoelectric generators. Nevertheless, compared to piezoceramic materials, PVDF based generators produce lower piezoresponse. Over the last decades, tremendous research activities have been reported to endorse the performance of PVDF based energy harvesters. This review article mainly focused on the recent progress in the performance improvement with processing methods, piezoelectric materials, different filler loading. The new developments and design structures will lead to an increase in piezoelectricity, alignment of dipoles, dielectric properties and subsequently enhance the output performance of the device. Electronic circuits play a vital role in energy harvesting to efficiently collect the developed charge from the device. Here, we have proposed a detailed description of the electronic circuits. Also, in the application part deals with the recent progress in flexible, biomedical and hybrid generators based on PVDF polymers.

Hydrogen storage at high pressure is currently attained by the use of different materials, such as elastomers in sealing joints, thermoplastics and thermosetting polymers in high-pressure containers, and metallic tube connections. Hydrogen containers type IV use a thermoplastic polymer for hydrogen tightness and composite materials for mechanical resistance, usually made with thermosetting resins and carbon or glass fibre. International standards impose a wide range of operative temperatures for such containers, from −40 °C to 85 °C. Once saturated with hydrogen at high pressure, a fast depressurisation process can create stress in the polymeric materials, causing its degradation by the formation of cavities. In a previous work, we were able to make a generalization of cavitation risk by the use of non-dimensional parameters, based on a simplified mechanical failure model. We observed that for the model, material's hydrogen diffusivity and yield strength are of upmost importance. In present work, we analyse the effect of temperature on these two properties, as they have an inverse evolution with temperature. Results confirm the pertinence of considering temperature in the whole application range of technology under analyse.

The end of life of carbon fibre-reinforced polymer (CFRP) structures represents a major challenge to the aerospace industry, as new European regulations are demanding recycling solutions that can be complicated and expensive to apply. This study aims to address new practical ways to recycle CFRP materials. CFRP materials with a polyether ether ketone (PEEK) matrix were fragmented via electrodynamical fragmentation, which exhibits several benefits compared to mechanical shredding processes, especially for composites commonly found in the aerospace industry. The fragments are characterized and reused to produce new CFRP aerospace parts. Structural testing of recycled composite parts revealed a 17% decrease of the mechanical properties compared to the novel material. The combination of these manufacturing and recycling techniques closes the cradle to cradle loop of thermoplastic CFRP.

International audience; This paper presents an experimental characterization of the damping capacity of the Fe-30Mn-6Si-5Cr subjected to cyclic tensile tests. Fe-SMA specimens underwent a specific heat treatment to improve their properties. At room temperature, the studied Fe-SMA showed different microstructures depending on the applied heat treatment. In order to define the best initial properties guaranteeing maximum pseudoelastic damping capacity (PDC), different types of initial microstructures were investigated: purely austenitic state and biphased states (austenite + stress induced and/or thermal martensite). The alloy was studied under different parameters such as loading-unloading frequencies, prestrain amount and operating temperatures. Experimental results were analyzed by computing the energy dissipated from hysteresis loops areas as well as the associated loss factor. Consequently, the beneficial role of the stress-induced martensite (${M}^{\sigma}$) was demonstrated and quantified. Furthermore, it was found that the PDC seems to have slightly improved by the presence of thermal martensite (Mth) and increased with temperature increase. As a result, an economical and efficient initial microstructure for damping application of the studied SMA has been defined.

This paper focuses on the mechanical behaviour of PP/MWCNT composites. The Young’s modulus and the rupture strain versus nanotubes content are investigated. Four grades are made: 1 wt%, 2 wt%, 4 wt%, 8 wt%. The achievement of the tensile test samples require three phases: the mixing stage, the identification of the rheological behaviour stage and the injection molding stage. In the mixing stage, one must be careful that there’s a good dispersion of the MWCNT in the polymer matrix. The rheological behaviour of the PP/MWCNT composite show that the useful injection molding parameters of the neat PP can be reinvestigated for the PP/MWCNT composites. Results of the mechanical experiments clearly show a high dependence of the Young’s modulus and the rupture strain with the CNT content.

International audience; This study aims to describe the response of a Hydrogen solid storage cylindrical tank, which is filled by a metal hydride alloy (FeTi-X) and subjected to several types of solicitations, such as: pressure, external temperature, and inlet and outlet flow. The model used in this work is classified as a macro scale model [1-2] it describes the Hydrogen absorption and desorption processes, and predicts the time-space profile of: local temperature, local reaction rate, local equilibrium pressure, local heat generated/needed, and then the homogeneous temperature, equilibrium pressure and reaction rate temporal profiles can be computed. In addition, the effect of cycling (absorption/desorption) on thereaction rate is monitored in order to optimize the operation and get at the same time a sufficient outlet flux coupled with a high reaction rate.

Sintered bulk ceramics, such as PZT are brittle materials. This macroscopically implies a statistical distribution of the ultimate strengths, because defects, such as pores or cracks are responsible for the initiation of the specimen failure. Another aspect of this fracture phenomenon is the crack propagation inside the material, along grain boundaries or through the grains themselves. An experimental study was carried out on hard and soft PZT by means of a scanning electron microscopy (SEM) quantitative analysis of tensile fractured areas. This reveals that the fracture mode is mixed, although it seems to be rather intragranular for hard ceramics and more intergranular for soft ones. Further investigations deal with the characterization of the residual porosity, which has to be distinguished from the population of critical defects. This porosity is located at grain boundaries and likely acts also as a stress concentrator and has an effect on the fracture mode and mechanical properties. For doped hard and soft PZT, a careful analysis of the microstructure is thus achieved through transmission electron microscopy (TEM) micrographs. Furthermore, domain structure is analysed for hard and soft PZT.

The aim of this work is to characterize the interface between a shape memory alloy wire (SMA) and a resin epoxy matrix. More precisely, we want to associate the roughness of the wire with the adhesion between the fiber/matrix. The effect of various surface treatments applied to SMA NiTi wires on the quality of the fiber/matrix interface is presented and discussed. First, a profilometric study is carried out on the different wires. The parameters, which characterize the vertical distribution of the roughness and the wire morphology, are determined. The topographic study reveals that the surface treatments which are applied strongly modify the external surface of the wire. In the second part of this work the adhesion fiber/matrix is quantified by using a pull-out test. These experimental results are analyzed and compared with the roughness parameters. This comparative study enables us to determine the wire morphology which will guarantee the best adhesion fiber/matrix. The roughness parameters are sufficient for the choice of the wire which will be embedded into the resin.

International audience; This paper focuses on the numerical simulation of the polypropylene / multi-walled carbon nanotubes (PP/MWCNT) flow into a twin screw mixer, during the mixing phase. The PP/MWCNT behavior obeys an innovating Carreau law enriched temperature built on the rheological properties carried out previously. The polypropylene was mixed with different MWCNTs contents (1, 2, 4 and 8 wt% of MWCNT content) and the rheological tests were performed at shear rate ranges from 10 to 210 s at four temperatures (180, 200, 220 and 240 °C). Thus the effects of the temperature and the MWCNTs content on the rheological properties of the PP/MWCNT composites were investigated. The finite element (FEM) analysis of the PP/MWCNT flow allows to compute the velocity, the shear rate and the temperature during the mixing phase period. A good agreement between the experimental measured torque on the screw and the calculated one is shown. Therefore, one can consider that the physical flow is generally well described, awaiting a numerical simulation of the PP/MWCNT mixing phase.

Electrical boundary conditions influence the nonlinear electromechanical behavior of ferroelectric materials. In this study, a hard and a soft PZT are tested under tensile loading in short and open circuit. Depolarization of the specimen or evolution of the electric field due to the piezoelectric effect is recorded. Nonlinear stress–strain curves are greatly affected by the electric field which appears in open circuit and reduces ferroelastic domain switching.

The compressive creep behaviour of a soft PZT has been studied. The effect of polarisation is measured and simulated by means of a viscoplastic-type model. The creep strain is linked to the amount of ferroelectric domains available to 90° ferroelastic switching. A temperature rise is found to reduce the anelastic strain but increase the creep strain itself.

The aim of this work is to collect a database from uniaxial experiments and model the material behavior. A soft PZT is tested in compression; the influence of stress rate seems to be negligible and the material accommodates to cyclic mechanical loadings. These responses are simulated by means of a phenomenological model taking into account the coupling between remnant strain and polarization thanks to a mechanically induced depolarization function.

The aim of this paper is to model the one-dimensional behaviour of a soft PZT tested in compression. Thanks to a viscoplastic formulation, the effects of cyclical loading and loading rates are also taken into account. The coupling between remnant strain and polarisation is achieved through a mechanically induced depolarisation function.